Metal-Insulator-Metal (MIM) capacitors are capacitor structures formed between the interconnection layers of semiconductor devices. The Metal-Insulator-Metal capacitors are massively applied in CMOS devices such as RFICs (Radio-Frequency Integrated Circuits) and semiconductor memories due to the satisfying compatibility with the back-end-of-line (BEOL) processing during the semiconductor manufacturing.
Taken a MIM capacitor structure defined by 2 masks as an example, it comprises from top to bottom a first metal layer, a dielectric layer, a top plate, an insulation layer, a bottom plate, a dielectric layer and a second metal layer. The top plate and bottom plate can be led out to form the positive and negative poles through vertical via interconnections or BEOL line.
Considering that processing problems or defects during the MIM capacitor preparation process may cause breakdown or current leakage of the MIM capacitor, an effective measurement should be taken to determine whether an electric leakage exists in the MIM capacitor.
A semiconductor structure for testing a MIM capacitor in the prior art is provided. As shown in FIG. 1, in the semiconductor structure, a first metal layer 110 is configured to be an upper layer of the structure, comprising a first circuit area 1100 and a second circuit area 1101. A second metal layer 111 is located right below the first metal layer 110, and separated from the first metal layer 110 by a dielectric layer 112 located therebetween. A top plate 120 and a bottom plate 121 are oppositely disposed within the dielectric layer 112 without contacting the first metal layer 110 and the second metal layer 111 respectively. The top plate 120 is separated from the bottom plate 121 by an insulation layer 122 located therebetween. The first circuit area 1100 is connected with the top plate 120 through a circuit connection 130, for example a vertical via interconnection or BEOL line, and the second circuit area 1101 is connected with the bottom plate 121 through a circuit connection 131 as well. The first metal layer 110 and the second metal layer 111, together with the insulation layer 122, form a MIM capacitor.
On one hand, since the conventional MIM capacitor is enclosed within insulating medium, the electric leakage regions existing in the insulating medium between the top plate and bottom plate is difficult to be detected through a voltage contrast mode due to the lack of a leakage path formed straight to the substrate. Therefore, it is hard to position the electric leakage regions in the MIM capacitor especially in large-size MIM capacitor.
On the other hand, by adopting a method of successively removing the layers covering the top plate of the MIM capacitor and then scanning the top plate in voltage contrast mode, unusual images representing obvious electric leakage regions can be observed. But for a slight electric leakage, it doesn't work well.
Thus, there is a need to design a semiconductor structure for detecting the electric leakage regions in a MIM capacitor completely and accurately.